As an enclosure bag for enclosing a positive electrode, a negative electrode, electrolytic solution and so on constituting a non-aqueous electrolyte battery and taking out each of the lead wires for the positive and the negative electrode to the outside and for enclosing also these lead wires, a composite material laminated with a plastic in which a metal foil or a vacuum-deposited metal layer is interposed in a sandwich-like form is used. Such an enclosure bag requires that the plastic held contacting with the electrolytic solution on at least inner side does not dissolve in the electrolyte, so that an enclosure bag is proposed, in which the sealing reliability is remarkably increased by using a maleic acid-modified polyolefin resin for the inner most layer and by constructing the heat sealing part by this maleic acid-modified polyolefin resin (Japanese Patent Kokai Hei 9-283101 A).
The maleic acid-modified polyolefin resin is superior in the adhesion onto metal and in the heat-sealing performance, so that it is used in general as an adhesive resin. When, however, it is attempted to use the maleic acid-modified resin as a sealing film for batteries, as mentioned above, an interlayer separation may occur after the film is held continued in contact with the electrolytic solution and it cannot be used as a sealing film, though it exhibits superior adhesive strength directly after it is laminated with metal.
A non-aqueous electrolyte is one in which a salt is dissolved in an organic polar solvent. The reason of occurrence of the interlayer separation is assumed to be due to that the organic polar solvent and the salt will penetrate through the maleic acid-modified polyolefin layer and reach the metal layer to cause a reaction with the metal, since the maleic acid-modified polyolefin and the salt have an affinity to the maleic acid-modified polyolefin resin which is polarized by maleic acid. Conventional laminates have a problem that such an interlayer separation cannot be avoided. Further, it is necessary to attach a protective film to the positive and negative electrodes, since they are metal and subject to a possibility of occurrence of short-circuit. Here also a problem occurs in which the protective film peels off due to the same reason as the sealing film.
The object of the present invention is to provide a laminate to be served as seal film for sealing the electrolyte of battery or as protection film for protecting the electrode part of battery, in particular, for sealing the electrolyte of secondary battery or as protection film for protecting the electrode part of secondary battery, which laminate is superior in the adhesive strength between the metal layer and the adhesive resin layer and in the fastness to organic polar solvents or to salts and which does not suffer from interlayer separation even when being held in contact with a non-aqueous electrolyte or the like, and a process for its efficient production as well as its uses, in order to solve the problems mentioned above.